1. Field of the Invention
The present invention relates to a method for transmitting data including images during communication and streaming among a plurality of terminals, a data transmission apparatus such as a mobile phone, a PDA, a TV telephone terminal, and a PC terminal, and a data transmission system.
2. Description of the Related Art
As a communication service for communications and streaming among a plurality of terminals, there is for example, as illustrated in FIG. 1, the visual communication service for transmission of data and images by mobile terminals (MT) comprised of portable phones.
The visual communication service system 1 compresses voice and images and exchanges signals between a mobile terminal (hereinafter simply referred to as a “terminal”) 2-1 and terminal 2-2 through a transmission channel 3 to enable conversation to be enjoyed while viewing the other party's face.
Each of the terminals 2-1 and 2-2, whose appearances are illustrated in FIG. 1, has a body case 21, an operation panel 22 provided at the lower portion of the body case 21 and including a keypad for inputting a telephone number for a call function or for inputting certain operational instructions, a display monitor 23 provided above the operational panel 22, a camera 24 provided above the display monitor 23 (at the upper portion of the body case 21), and an antenna 25.
The transmission channel 3 includes mobile base stations (MBS) 31-1 and 31-2, mobile switching centers (MSC) 32-1 and 32-2, gateway mobile switching centers (GMSC) 33-1 and 33-2 having home location registers (HLR), and a circuit network 35.
The mobile base stations 31-1 and 31-2 communicate with the terminals 2-1 and 2-2. The signals handled by the base stations 31-1 and 31-2 are sent to the higher level mobile switching centers 32-1 and 32-2 and further to a backbone circuit network 35 through the higher level gateway mobile switching centers 33-1 and 33-2.
When transmitting images to such a circuit network 35, however, the information carrying capacity of the circuit network 35 is limited by the bandwidth of the circuit network 35.
Therefore, a user who is talking using for example the terminal 2-1 can view his or her own image captured by the camera 24 at a high quality such as with the image shown by 23a in FIG. 1 because the image is monitored directly, but after compression at the terminal 2-1 and transmission to the terminal 2-2, the quality of the image sent from the terminal 2-1 becomes extremely degraded at the terminal 2-2 such as shown by the image shown by 23b. 
Similarly, at the terminal 2-1, the quality of the image sent from the terminal 2-2 to the terminal 2-1 becomes extremely degraded.
In this way, in an image transmission system of the prior art, the transmitted images become extremely degraded. The difference from the image which the user himself or herself monitors becomes too great. This causes not only a strong uncomfortable feeling but also a feeling of stress as the expression of the other party cannot be seen clearly.
Further, in each of the terminals 2-1 or 2-2, the camera 24 is located above the display monitor 23 of the terminal. The users look at their display monitors 23 of their terminals. Therefore there is the problem that both end up looking down and therefore conversation maintaining eye contact becomes impossible.